In history class, the girl to boy ratio is $2$ to $10$. If there are a total of $60$ students, how many girls are there?
Solution: A ratio of $2$ girls to $10$ boys means that a set of $12$ students will have $2$ girls and $10$ boys. A class of $60$ students has $5$ sets of $12$ students. Because we know that there are $2$ girls in each set of $12$ students, the class must have $5$ groups of $2$ girls each. There is a total of $10$ girls in history class.